1. Field of the Invention
This invention relates to drills for use in metal, and in particular to drills designed for high feed rates that place a premium upon resistance to bending.
2. Background and Description of Related Art
When operating at the very high metal removal rates desirable in high production drilling, the heaviest component of the reaction to the cutting force has been found to be axial in nature, amounting, in some instances, to ninety percent (90%) of the cutting force. In this kind of service, the maintenance of tolerances on hole size is largely dependent upon the resistance of the fluted drill body to both bending and buckling under the cutting load, which, even with the rarely achievable balanced distribution of the transverse cutting forces, is largely a question of the stiffness of the fluted drill body, as a beam and as a column, under the major load components resulting from high feed rates.
The problem of deflection of metal drills has largely been addressed in the prior art as one of balancing the transverse forces upon the cutting tip for the elimination, to the extent possible, of a transverse resultant. While some prior art drills have approached desirable stiffness by shortening the fluted drill body, the significant criteria for drill stiffness appear to have remained undiscovered by the prior art.